In accordance with the conventional powder metallurgy method of producing sintered articles, a metal or alloy powder as a composition to be shaped is press-shaped and then the resulting green body is sintered to form a sintered article. Therefore, it was difficult to produce articles having three-dimensionally complicated shapes, thin articles or articles having a thin part such as a knife edge part by the said method.
In order to overcome the drawback of the above-mentioned method, a different method has been proposed wherein an injection-mouldable composition which is composed of a metal or alloy powder and a binder is injeciton-moulded into a mould having a determined shape and the thus moulded green body is heated to remove the binder therefrom and thereafter sintered to form a metal or alloy-sintered article (Japanese Patent Application Laid-Open Nos. 57-16103 and 57-26105).
Since the method uses a metal or alloy powder having a mean particle size of 10 .mu.m or less, an article having a high sintered density can be obtained. However, the method requires a long period of time for the step of removing the binder from the green body. As a result, the method has an economical disadvantage that the manufacture cost is high.
If a rapidly decomposing binder is employed for the purpose of shortening the time for removing the binder, the shaped green body would be cracked, blistered or deformed in the binder-removing step because of the gas to be caused by decomposition of the binder. As opposed to this, a trial of using a mixture comprising a slow-decomposing binder and a rapidly decomposing binder in a desired proportion has been effected. Even in such trial, however, the binder-removing property of the green body could not be improved.
The improvement of the binder-removing property as referred to herein means that the time necessary for completion of removal of binder is short, the processing temperature for removal of binder may be low, and the green body is free from defects of cracking, blistering, deformation or the like during the binder-removing step.
Under the situtation, the object of the present invention is to provide an injection-mouldable composition for producing precision parts, which comprises a metal or alloy powder as the raw material and which is characterized by the improved binder-removing property. None of the conventional injection-mouldable compositions could have such improved binder-removing property.